Estimating Onsets of Binary Events in Panel Data

Onsets of binary events are often of interest to political scientists, whether they be regime changes, the occurrence of civil war, or the signing of bilateral agreements, to name a few. Often researchers transform the binary event outcome of interest, by setting ongoing years to zero, to create a variable which measures the onset of the event. While this may seem an intuitive way to go about estimating models where onset is the outcome of interest, it results in two problems that can affect substantive inferences. First, it creates two qualitatively different meanings for a unit time period to have a zero, which estimators are unable to “know.” Second, it ignores the possibility that variables may have differing effects upon binary event onsets and durations. This article explores how much this transformation can harm our substantive inferences by analytically demonstrating the resulting bias and the use of Monte Carlo experiments, as well as offering recommendations to avoid these problems. I also conduct a sensitivity analysis on the determinants of civil war onset to examine how substantive inferences are affected by this issue. In doing so, I find that there is considerable difference in the size of estimated coefficients and whether a variable is considered a robust determinant of civil war.